The present invention is directed to a method of treating exhaust gases containing halogen compound (halogen or halide), for example, halogen gase and halogenated acid gas such as hydrogen halide, and in particular to a method of removing and detoxifying exhaust gases containing halogen compound discharged from the dry etching process and so on during the manufacture of semiconductors.
In the semiconductor industry, many kinds of corrosive gases are used to manufacture semiconductors. They are highly toxic, and can contaminate the environment. The exhaust gases discharged during dry etching containing halogen compound which are detrimental to human bodies. Besides, they are corrosive, causing problems in corroding devices in the vacuum system when combined with any moisture present in the system. Thus, it is a pressing issue to establish a system for removing these gases. Several methods have been suggested to remove these halides, such as those disclosed in patents, Japanese Patent Opening Nos.6-198128, 6-47233, and 4-94723. These patents suggest methods of removing halide gases using the following treatment agents (1) to (5).
(1) Metal oxides (oxides of several metals)
(2) Activated carbon or activated carbon carrying medicines (such as activated carbon carrying alkali metal oxides as adsorbent)
(3) Alkalis (Ca(OH)2, Mg(OH)2, CaO, MgO, etc.)
(4) Oxidizing agents (KMnO4, etc.)
(5) Combination of the above (1) to (4)
Halide gases discharged during dry etching are roughly classified by their natures into the following groups.
(1) Halogen gases (F2, Cl2, Br2)
(2) Hydrogen halide gases (acid gases) (HF, HCl, HBr)
(3) Others
Generally, it is rare that a single gas is discharged. Usually, more than one gas is discharged mixed together.
Among these halides, (1) and (2) generate most problems. They should be not only completely treated because they are harmful to human bodies and the environment, but also they are corrosive gases to combine with moisture in the system to corrode equipment (dry pumps, metal components of rotary pumps, and metal plumbings) in the vacuum system.
Corrosion of equipment will reduce the stability of the vacuum system, make it difficult to support the conditions for manufacturing semiconductors, and incur considerable costs in replacing corroded components.
With the conventionally proposed detoxifying (treating) agents such as metal oxides (Fe2O3 as an example), the metal oxide reacts with an acid gas to generate water as follows:
Fe2O3+6HClxe2x86x922FeCl3+3H2O
As stated above, water is detrimental because it causes corrosion in the system. Similarly, alkalis and oxidizing agents are detrimental because they react with an acid gas to generate water. Activated carbon cannot treat the acid gas sufficiently. Therefore, it is necessary to provide the vacuum system with a system that reacts with or adsorbs acid gases and halogens (physical adsorption, reactive adsorption) without generating water. But there is no such system based on the prior arts.
The purpose of the present invention is to provide a method of effectively removing halogen compounds such as acid gases and halogen gases, as stated above, from exhaust gases.
The present invention relates to a method of treating exhaust gases containing halogen compounds, the improvement in that simple metals are employed to come into contact with the exhaust gases containing the halogen compounds such as halogen gases and/or hydrogen halides (halogenated acid gases).
According to the treatment method of the present invention, simple metals are used as agents for treating exhaust gases. These metals react with the halogen compounds as shown in the following formulas, thereby removing corrosive, harmful halides, without generating water, and avoiding corrosion effectively within the system as the following formulas:
2Fe+6HClxe2x86x922FeCl3+3H2
2Fe+3Cl2xe2x86x922FeCl3
In the treatment of the present invention, the simple metals include tin, lead, zinc, zirconium, iron, nickel, molybdenum, manganese, tantalum, and cobalt, and at least one of these should be used.
It is advantageous for facilitating reaction to bring exhaust gases containing halogen compounds into contact with such simple metals at 20 to 300xc2x0 C. (preferably 100 to 300xc2x0 C.).
The simple metals may be of any shape: granule, bar or sheet, as long as they are operable. The size of metal should preferably be as large as possible to increase the contact area unless ventilation resistance increases when the exhaust gases pass. A single simple metal or more than one simple metal may be used at one time.
Contact between the exhaust gases and the metals is realized by filling the metals according to the gas load in a packed tower and introducing the gases into the tower to bring them into contact with the metals.
The actual points at which the exhaust gases are to be removed during dry etching in the manufacture of semiconductors may be as follows.
a) Between the vacuum pump and the reactor
b) Between the vacuum pump and the exhaust gas outlet
c) If an oil-sealed rotary vacuum pump is used, the pump oil is circulated and passed through the packed tower as above to remove dissolved gas within the vacuum pump oil.
Items a) and c) above are provided to protect the vacuum pump from corrosion, and b) is to avoid discharge of the exhaust gases into the environment.
As a toxicity removing (treating) agent, the above simple metals and activated coal can be combined in use.
Because the treatment method of the present invention uses simple metals as an agent for treating exhaust gases, the metals react with halogen compounds, for example, as shown in the above formulas, not only removing corrosive and harmful halogen compounds without generating water, but also effectively preventing corrosion from occurring in the system.
Now several examples of the present invention will be described. They will not limit application of the invention.